The mint I used was just one of those little four inch pots from the grocery store, you know the kind? I was using it as a houseplant and decided to try it in a few of the potted shrubs when it got warm. Just put a few sprigs with a few tiny root hairs in each potted plant.
by autumn some of those roots were an inch and a half thick. I have never seen anything grow so quickly and get so big and sprawling so fast.
I was so glad it died over the winter. I would never have been able to get rid of it from those potted shrubs.
I have heard many horror stories about it, but then again, every now and then someone does seem to be able to grow it with it just spreading a bit and not being too invasive. I have no idea of why it sometimes just behaves differently like that. Same varieties and all..and sometimes it is just fine.
I would not chance it in the ground though around here.